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Trypanosomes have a novel form of mitochondrial DNA, termed kinetoplast DNA (kDNA), which consists of several thousand minicircles and a few dozen maxicircles, all of which are topologically interlocked in a single disc-shaped network. Hines and Ray (p. 1319-1328) report the identification of mitochondrial DNA primase PRI1, which is required for cell growth and for maintenance of the kDNA. PRI1 is essential for maxicircle DNA replication and secondarily needed for minicircle replication. The addition of PRI1 to the repertoire of known mitochondrial replication proteins in trypanosomes will facilitate direct studies of the mechanism of initiation of maxicircle DNA replication.
The detailed mechanism of ubiquitin-independent degradation of p21 remains elusive. Wang et al. (p. 1508-1527) have uncovered a critical role for 14-3-3τ in this process. 14-3-3τ binds p21, MDM2, and the C8 subunit of the 20S proteasome in G1 phase and facilitates proteasomal degradation of p21 in a ubiquitin-independent manner. Importantly, overexpression of 14-3-3τ is frequently seen in human breast cancer and is associated with a low p21 level and shorter patient survival. Through regulation of p21 degradation, 14-3-3τ also controls the hormone response in breast cancer. Their data suggest that 14-3-3τ may be a new therapeutic target for breast cancer.